1. Field of the Invention
The present invention relates to devices known as taps designed to control the flow of a fluid, generally water, from a shut-off position up to a maximum flowrate adapted to the users' needs.
2. Description of the Prior Art
The commonest taps comprise a fixed seat in which is a circular opening for the liquid to pass through. A movable rubber valve member is moved by an operating handle of the tap, perpendicular to the surface of the seat. The flowrate is adjusted by varying the distance between the surface of the seat and the mobile valve member.
This type of tap has numerous disadvantages:
rapid wear,
imprecise position of the valve member, and therefore of the associated operating handle, when the tap is closed,
performance varying with time, etc.
For this reason a new generation of products has been developed, utilizing ceramic plates. Their operating principle is as follows:
Two disks, generally of alumina, comprise one or more sector-shaped openings and each has at least one extremely flat and highly polished side.
The sectors are substantially identical and equal in number on the two disks, occupying angular positions adapted to come into corresponding relationship at a specific relative angular position of the two disks.
These two disks are superposed with the polished sides in contact and the fluid whose flowrate is to be controlled is fed in behind one of the two disks, which is usually fixed.
A mechanical device coupled to the operating handle of the tap rotates one of the disks relative to the other.
According to whether the openings are made coincident or not, the fluid is allowed to pass through or not. The flowrate is adjusted according to the amount the openings overlap.
Taps of this type are described in document US-A-2.165.639, in particular.
Most products available on the market comprise one or two openings in each disk respectively delimited by one or two straight line segments parallel to diameters of the disk and a circular arc concentric with the perimeter of the disk.
In the case of disks with one opening, the shape of the latter is approximately that of a half-disk. The maximum flowrate is obtained for a rotation of 180.degree.. By extension, these taps are known as "half-turn" taps.
In the case of disks with two openings, the shape used is approximately that of a quarter-disk. The maximum flowrate is obtained for a rotation of 90.degree.. By extension, these taps are known as "quarter-turn" taps.
In both cases the shape of the openings is symmetrical and can always be bisected by a line passing through the center of the disk.
These taps have several disadvantages:
an insufficient range of adjustment, for which the theoretical maximum is 180.degree. and the practical limit much smaller because of problems with overlapping; note that the sectors on either disk cannot occupy in total more than 180.degree.. since there must be a configuration in which the sectors do not overlap at all;
imprecise adjustment at extreme values, especially at low flowrates;
problems with obtaining linear adjustment because of the symmetry of the openings, which means that the equation giving the flowrate of the tap head cannot take into account parameters other than the water passage cross-section;
unavoidable noise in some operating positions because the shape of the water passage or passages resulting from partial overlapping of the openings comprises during all or part of the rotation an acute angle generating disturbances in the flow of the fluid.
Two European patents, Nos. 33.428 and 55.181, filed in the name of the assignees of this application describe improvements to such devices relating to reducing the flow noise under steady conditions and during operations to vary the flowrate. These documents teach only a partial solution to the aforementioned disadvantages, however.
The present invention is directed to providing a more complete solution to the aforementioned disadvantages and in particular improved sensitivity of flowrate adjustment.
The invention is based on the observation that the performance of the product can be improved by dispensing with the symmetry of the openings themselves, and even with the identical angular size and disposition of these openings on each disk.
There is already known from document FR-A-910.720 an air flowrate control device comprising two disks each comprising a narrow fish-shaped opening of small angular size; these openings are adapted to be superposed head-to-tail so that the device constitutes a throttling device. There are also known from documents GB-A-1.549 789, US-1.751.591 and GB-A-881.325 liquid taps with a single disk facing an integral portion of of the tap body in which there is a small orifice; in each of these disks there is formed an elongate opening subtending an angle of more than 180.degree.. These documents teach very narrow openings spaced a long way in the radial direction from the center of the disk which lend themselves only to passing a maximum flowrate that is highly restricted for a given overall size. Nor do they meet the objectives of the invention, which are in particular to provide for a high flowrate.